1. Field of the Invention
The present invention relates to the field of backlight module of liquid crystal display device, and in particular to a light guide plate and a side-edge backlight module using the light guide plate.
2. The Related Arts
The increasingly improved performance of LED (Light-Emitting Diode) brings continuous progress of LED backlighting for television, from the very initial four-side light incidence, to two-side light incidence, and then to single-side light incidence. The contemporary development and future direction of progress are set in single short edge light incidence.
Further, with the progress of 3D technology, 3D displaying function is now the main stream. The commonly known 3D displaying modes include shutter glass and film-type patterned retarder (FPR).
The shutter glass 3D displaying is effected with scanning backlight in combination with panel pixel scanning. Backlighting is often sectionalized so that a side-edge LED light bar is divided into multiple sections. When a first frame signal of a panel is applied to scan the first section, the LEDs of the first section are lit, while the remaining is set off. When the panel signal scans the second section, only the LEDs of the second section are lit. This is also applied to other sections. Such an operation is carried out for each frame. The performance of the shutter glass 3D displaying is assessed according to cross-talking among sections. The lower the cross-talking is, the better the displaying result will be. Cross-talking is generally determined according to cross talk among the backlight sections and design of timing sequence.
Cross-talking among backlight sections generally comes from the influence of brightness among different sections and the best situation is that when one section is lit, the backlighting of all the remaining sections shows darkness. As shown in FIG. 1, a side elevational view of a conventional light guide plate with upper microstructures is illustrated. Forming serrated microstructures on the upper surface (light exit surface) of a light guide plate is a commonly known design. FIG. 1 is made for observation of light guide plate 10 from the side where light gets incident. The upper surface of the light guide plate 10 forms upper microstructures 11 distributed on the upper surface of the light guide plate 10 in a successive raising-recessing-alternating arrangement in a direction perpendicular to the propagation direction of light in the light guide plate 10, whereby the geometric variation on the upper surface of the light guide plate is useful to eliminate the conditions for occurrence of total reflection. As shown in FIG. 2, a schematic view illustrating difference of light shape between a conventional flat light guide plate and an upper-microstructured light guide plate is given. Although FIG. 2 illustrates that the light shape of the upper-microstructured light guide plate 20 shows more confined light shape than a flat light guide plate 21, yet actually, even though light in the upper-microstructured light guide plate 20 is partially confined, it gets diverging to some extents.
With the increase of the propagation distance, the divergence of the light shape gets greater and shows severer influence on other sections. As shown in FIG. 3, a schematic view showing the distribution of light field of a well known upper-microstructured light guide plate 30 for the condition of one section being lit is given. When one section of the upper-microstructured light guide plate 30 is lit, the light shape is getting divergent with distance. Referring to FIG. 4, which is a schematic view showing the distribution of brightness in a vertical direction for the light shape shown in FIG. 3, the brightness distribution in the vertical direction can be indicated by full width at half maximum (FWHM), left side being the light incidence side. Referring to FIG. 5, which is a schematic view showing the variation of the width for half brightness at different locations with respect to the distance, in a single short edge light incidence, FWHM shows a trend of getting wider with the increase of distance. In other words, for single short edge light incidence, the remote side shows severer cross-talking than the light incidence side. Referring to FIG. 6, a schematic view illustrating the distribution of cross-talking for 9 points on a backlight module including the upper-microstructured light guide plate of FIG. 3 in a 3D mode is given. The left hand side of FIG. 6 is the light incidence side and it is clear that the remote side has severer cross-talking.